Ball bearing and main shaft device for machine tool

ABSTRACT

When inner diameter side opening portions are projected on an outer circumferential surface of a retainer along extension lines of central lines of radial holes, at least parts of the inner diameter side opening portions of a plurality of radial holes of an outer ring are positioned within an area of two circles formed by connecting each of axial end portions of adjacent pockets of the retainer in an axial direction. When a central line of any one radial hole coincides with a circumferential phase of a center of a ball, any other radial hole is formed such that the projected inner diameter side opening portion is separated from the ball and an inner circumferential surface of the pocket when viewed from the radial direction of the ball bearing, and a central line of the other radial hole overlaps with the pocket when viewed from the axial direction.

TECHNICAL FIELD

The invention relates to a ball bearing and a spindle device for amachine tool, and particularly to an outer ring oil-supply type ballbearing and a spindle device for a machine tool.

BACKGROUND ART

In recent years, in a spindle for a machine tool, a demand forhigh-speed operation increases for improvement of cutting efficiency. Inaddition, recently, in the spindle, for improvement of productionefficiency, a need to correspond to a five-axis machining tool capableof machining a workpiece having a complicated shape without using aplurality of machine tools and without a changeover emerges. In thefive-axis machining tool, the spindle or the table turns. Thus, theshortening of the axial length of the spindle is required due to thedemands for the space saving by the shortening of the turning radius,the power saving by the inertia reduction in turning and the weightreduction, or the like.

Grease lubrication, oil-air lubrication, oil-mist lubrication or thelike is exemplified as a lubricating method which is widely adopted fora rolling bearing for the machine tool spindle. Generally, the oil-airlubrication is adopted in the area of high-speed rotation (dmn 800,000or more). As oil-air lubrication of the related arts, there is known asystem of supplying a high-pressure air and fine oil particles from aside surface of a bearing into the bearing by using an oil supplyingnozzle piece 101 arranged on the side of a bearing 100 illustrated inFIG. 9A or the oil supplying nozzle piece 101 inserted into a radialthrough-hole 102 a of an outer ring spacer 102 arranged on the side ofthe bearing 100 illustrated in FIG. 9B.

In this system, an oil supplying component such as the nozzle piece 101is required additionally, and the number of the spindles increases. Thisleads to an increase in the cost of the entire spindle and the effortfor management. In addition, since the nozzle piece 101 is used, theshape of the outer ring spacer and the structure of the housing becomecomplicated, and the effort of designing and machining the spindleincreases. Further, since the nozzle piece 101 is provided on the sidesurface of the bearing in the rotational axial direction, a certaindegree of the spacer length is required, and the axial length of thespindle is elongated. Accordingly, the size of the machine tool itselfincreases, the weight of the spindle becomes heavier as the axial lengthincreases, and the whirling speed (the whirling speed is a rotationalspeed calculated from the natural frequency of the spindle, and thevibration becomes large when the spindle is rotated in this whirlingspeed range) of the spindle decreases. In addition, the supply of oilparticles from the oil supplying nozzle is hindered by the air curtain(the air curtain is a wall of high-speed air flow in the circumferentialdirection generated by friction between air and the inner ring outerdiameter surface rotating at high-speed) generated by high-speedrotation. As a result, it is hard to reliably supply lubricating oilinto the bearing. As described above, the oil-air lubrication of therelated arts has such structural and functional problems.

As another oil-air lubrication system, as illustrated in FIG. 10, thereis known a system which uses an outer ring oil-supply type bearing 110in which an oil groove 112 is formed on the outer circumferentialsurface of the outer ring 111 in the circumferential direction, and aplurality of oil holes 113 directed in a radial direction are formed atthe same axial position as the oil groove 112 (for example, see PatentDocument 1). In such an outer ring oil-supply type bearing, even in acase where the bearing is used at high-speed rotation, the supply of theoil particles is not hindered by the air curtain. For this reason, it ispossible to stably use the spindle even at high-speed rotation.

FIG. 11 is a schematic view of the spindle in each case of the oil-airlubrication using the nozzle piece 101 and the oil-air lubrication withthe outer ring oil-supplying specification. The upper half of FIG. 11 isa spindle 120 of the oil-air lubrication with the outer ringoil-supplying specification, and the lower half is a spindle 120A of theoil-air lubrication using the nozzle piece 101. Incidentally, in FIG.11, reference sign 121 denotes a rotary shaft, and reference sign 122denotes a rotor of a motor fitted to the rotary shaft 121. In this way,when the oil-air lubrication uses the nozzle piece 101, a spacer havinga certain axial length or more is required to supply the lubricating oilfrom the side surface of the bearing 100. On the other hand, with theouter ring oil-supplying specification, an oil supplying spacer is notrequired. Thus, the nozzle piece can be reduced in size, and thestructure of the spacer can be simplified, and the axial length of thespacer 123 can be shortened compared to the case of the specificationusing the nozzle piece. Accordingly, in the outer ring oil-supplyingspecification, it becomes simple to design and machine the spindle andthe oil supplying component and manage the components, and the reductionof overall cost can be achieved in designing, manufacturing and managingof the machine tools. Additionally, the axial length can be shortened toreduce the size of the machine tool and improve the whirling speed ofthe spindle. As described above, the outer ring oil-supply type bearinghas many advantages compared with a conventional side surface oil-supplytype bearing.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2013-79711

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Incidentally, the ball bearing for the machine tool spindle is usedunder various conditions according to the specifications of the spindle.When the number of revolutions of the bearing or the initial preload andthe external load during machining are different, the internal state(the contact angle, the size of the contact ellipse of the contact partbetween the inner ring groove and the ball or the outer ring groove andthe ball, the contact pressure, or the like) of the used bearing isdifferent. For this reason, in the ball bearing to be used under variousconditions, it is desirable to improve the lubricity of the bearing.Particularly, it is desirable that the lubricating state of the slidingcontact part between the ball and the retainer is held excellentlyduring the high-speed rotation.

The invention has been made in consideration of the above-describedproblems, and an object thereof is to provide a ball bearing which isprovided in an outer ring of an outer ring oil-supply type bearing andin which excellent lubricity during high-speed rotation and low noiseand low vibration can be achieved by properly setting axial positionsand circumferential positions of a plurality of radial holes, and aspindle device for a machine tool.

Means for Solving the Problems

The above object of the invention is achieved with the followingconfiguration.

(1) A ball bearing including:

an inner ring with an inner ring raceway groove on an outercircumferential surface;

an outer ring with an outer ring raceway groove on an innercircumferential surface;

a plurality of balls which are arranged in a rollable manner between theinner ring raceway groove and the outer ring raceway groove; and

a retainer with a plurality of pockets for retaining the plurality ofrespective balls, wherein

the outer ring includes a plurality of radial holes which penetrate fromthe outer circumferential surface to the inner circumferential surfacein the radial direction to supply lubricating oil, such that the ballbearing is lubricated by the lubricating oil,

when inner diameter side opening portions of the plurality of radialholes are projected on an outer circumferential surface of the retaineralong extension lines of central lines of the racial holes, at leastparts of the projected inner diameter side opening portions arepositioned within an area of two circles formed by connecting each ofaxial end portions of respective pockets of the retainer in a rotationalaxial direction of the ball bearing, and

when the central line of any one radial hole among the plurality ofradial holes coincides with a circumferential phase of a center of theball, any other radial hole is formed such that when the inner diameterside opening portion of the other radial hole is projected on the outercircumferential surface of the retainer along the extension line of thecentral line of the radial hole, the projected inner diameter sideopening portion is separated from the ball and the inner circumferentialsurface of the pocket when viewed from a radial direction of the ballbearing, and the central line of the other radial hole overlaps with thepocket when viewed from the axial direction of the ball bearing.

(2) The ball bearing according to (1), wherein

a concave groove communicating with the radial hole is formed along acircumferential direction in an outer circumferential surface of theouter ring.

(3) The ball bearing according to (2), wherein

in the outer circumferential surface of the outer ring, annular groovesare formed on both axial sides sandwiching the concave groove along thecircumferential direction, and annular seal members are respectivelyarranged in each of the annular grooves.

(4) The ball bearing according to any one of (1) to (3), wherein

a diameter of the radial hole is 0.5 to 1.5 mm.

(5) The ball bearing according to any one of (1) to (4), wherein

in the radial hole, an opening area of the inner diameter side openingportion is larger than an opening area of the outer diameter sideopening portion.

(6) A spindle device for a machine tool including:

the ball bearing according to any one of (1) to (5).

Effect of the Invention

According to the ball bearing of the invention, the outer ring includesthe plurality of radial holes which penetrate from the outercircumferential surface to the inner circumferential surface in theradial direction to supply the lubricating oil. When the inner diameterside opening portions of the plurality of radial holes are projected onthe outer circumferential surface of the retainer along the extensionline of the central lines of the radial holes, at least parts of theprojected inner diameter side opening portions are positioned within thearea of two circles formed by connecting the axial end portions of thepockets of the retainer in the rotational axial direction of the ballbearing. In addition, when the central line of any one radial hole ofthe plurality of radial holes coincide with the circumferential phase ofthe center of the ball, any other radial hole is formed such that whenthe inner diameter side opening portion is projected on the outercircumferential surface of the retainer along the extension line of thecentral line of the radial hole, the projected inner diameter sideopening portion is separated from the ball and the inner circumferentialsurface of the pocket when viewed from the radial direction of the ballbearing, and the central line of the other radial hole overlaps with thepocket when viewed from the axial direction of the ball bearing.Accordingly, the lubricating oil is supplied from any one radial hole tothe sliding contact part between the ball and the retainer, and alsofrom any other radial hole, sufficient lubricating oil is supplied tothe sliding contact part between the ball and the retainer through theouter circumferential surface of the retainer. Therefore, the excellentlubricating state can be maintained to prevent the seizure of thebearing. In addition, the noise and the vibration can be reduced withoutcompletely blocking the flow of the compressed air.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a ball bearing according to one embodimentof the invention.

FIG. 2 is a sectional view of the ball bearing as seen along line II-IIof FIG. 1.

FIGS. 3A to 3C are views illustrating a ball and a retainer when viewedfrom the outer diameter side, wherein FIG. 3A illustrates the conditionof the area where the inner diameter side opening portion of the otherradial hole can be arranged, FIG. 3B illustrates the condition of thearea where the central line of the other radial hole can be arranged,and FIG. 3C illustrates the area where the inner diameter side openingportion of the other radial hole can be arranged in consideration ofboth conditions of FIGS. 3A and 3B.

FIG. 4A is a sectional view of the ball bearing illustrating the axialoutermost position of the radial hole on a counter bore side, and FIG.4B is a sectional view of the ball bearing illustrating the axialoutermost position of the radial hole on a side opposite to the counterbore side.

FIG. 5 is a sectional view of a ball bearing according to a firstmodification of the present embodiment.

FIG. 6 is a sectional view of a ball bearing according to a secondmodification of the present embodiment.

FIG. 7 is a sectional view of a ball bearing according to a thirdmodification of the present embodiment.

FIG. 8A is a sectional view of a ball bearing according to a fourthmodification of the present embodiment, and FIG. 8B is a sectional viewof a ball bearing according to a fifth modification of the presentembodiment.

FIGS. 9A and 9B are a sectional view illustrating a oil-air lubricationof the related arts using a nozzle piece.

FIG. 10 is a sectional view of the ball bearing of the oil-airlubrication with an outer ring oil-supplying specification.

FIG. 11 is a sectional view in which the upper half is a spindle of theoil-air lubrication with the outer ring oil-supplying specification, andthe lower half is a spindle of the oil-air lubrication using the nozzlepiece.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a ball bearing and a spindle device for a machine toolaccording to one embodiment of the invention will be described in detailbased on the drawings.

As illustrated in FIG. 1, an angular ball bearing 10 according to thepresent embodiment is applicable to a spindle device for a machine tooland includes an inner ring 11 with an arc-shaped inner ring racewaygroove 11 a on the outer circumferential surface, an outer ring 12 withan arc-shaped outer ring raceway groove 12 a on the innercircumferential surface, a plurality of balls 13 which are arranged witha predetermined contact angle α in a rollable manner between the innerring raceway groove 11 a and the outer ring raceway groove 12 a, and anouter ring guide type retainer 14 with a cylindrical pocket P forretaining the plurality of balls 13. A counter bore 12 b with aninclined part of which the diameter reduces gradually from the axial endsurface to the outer ring raceway groove 12 a is provided on one innercircumferential surface of the outer ring 12 in the axial direction, anda groove shoulder 12 c having a uniform inner diameter is formed on theother inner circumferential surface in the axial direction. In thepresent embodiment, the outer circumferential surface 14 a of theretainer 14 is formed to have a uniform outer diameter in the axialdirection.

The angular ball bearing 10 is an outer ring oil-supply type bearing,and the outer ring 12 includes a plurality of radial holes 15 (15 a, 15b) which penetrate from the outer circumferential surface to the innercircumferential surface in the radial direction to supply lubricatingoil. In addition, concave groove 16 which communicate with the pluralityof radial holes 15 are formed on the outer circumferential surface ofthe outer ring 12 along the circumferential direction. Accordingly, inthe angular ball bearing 10, oil particles and lubricating air which aresupplied from an oil supply passage of a housing (not illustrated) aredirectly supplied to the ball 13 through the concave groove 16 and theradial hole 15 of the outer ring 12, and oil-air lubrication isperformed.

Incidentally, instead of being provided in the outer ring 12, thecircumferential concave groove may be formed at the position of the oilsupply passage opening communicating with the radial hole 15 in theinner circumferential surface of the housing.

In this way, the plurality of radial holes 15 are provided so that thelubricating oil can uniformly spread over the entire raceway surfacewithout unevenness, and the reliability of the lubrication during thehigh-speed rotation can be improved.

In addition, the outer ring 12 is well cooled in a phase close to theradial hole 15, and the cooling is weak in the phase far from the radialhole 15. Thus, a temperature difference is generated by the phase of theouter ring 12 to affect the dimensional accuracy of the bearing. Forthis reason, the plurality of radial holes 15 are provided so that thetemperature fluctuation of the outer ring 12 of the bearing can beprevented.

As illustrated in FIG. 2, in the present embodiment, when the innerdiameter side opening portions 30 of the plurality of radial holes 15are projected on the outer circumferential surface of the retainer 14along the extension lines of the central lines X1 and X2 of the radialholes 15, at least parts of the projected inner diameter side openingportion 30 are positioned within the area (in a dotted line Sillustrated in FIG. 1) of two circles L (see FIGS. 3A to 3C) formed byconnecting each of the axial end portions of the respective pockets P ofthe retainer 14 in the rotational axial direction of the ball bearing10.

Generally, the sliding contact part (the inner surface of the pocket Pof the retainer 14) between the ball 13 and the retainer 14 is in a badlubricating state. Particularly, in the bearing for the machine toolspindle, in order to avoid the temperature increase and the temperaturefluctuation of the bearing, the amount of the lubricating oil suppliedto the bearing is extremely small. Under such conditions, sufficientlubricating oil is hardly supplied to the sliding contact part betweenthe ball 13 and the retainer 14, and the seizure may occur due to thelubrication failure of the sliding contact pan between the ball 13 andthe retainer 14.

Therefore, it is desirable that the lubricating oil is supplied to theouter ring oil-supply type bearing such that the lubricating state ofthe sliding contact part between the ball 13 and the retainer 14 ismaintained excellently. For this reason, when the inner diameter sideopening portions 30 of the radial holes 15 are projected on the outercircumferential surface of the retainer 14 along the extension lines ofthe central lines X1 and X2 of the radial holes 15, the projected innerdiameter side opening portions 30 are positioned within the area of twocircles L formed by connecting each of the axial end portions of therespective pockets P of the retainer 14 in the rotational axialdirection of the ball bearing 10. Thus, sufficient lubricating oil issupplied to the sliding contact part between the ball 13 and theretainer 14, to maintain the excellent lubricating state and prevent theseizure of the bearing.

If the inner diameter side opening portions 30 of the above-describedprojected radial holes 15 are outside the above-described area of thetwo circles, the vibration and the noise increase as well as thelubrication failure occurs in the sliding contact part between the ball13 and the retainer 14. Specifically, the pressure of the compressed airacts on a point separated from the axial central position of theretainer 14, to generate a couple of force to incline the posture of theretainer 14. Desirably, the retainer 14 in the bearing during therotation is typically rotated in the same posture. However, the postureof the retainer 14 is changed with time by the couple of force, and thevibration or the noise caused by the movement of the retainer 14increases.

In the present embodiment, at least parts of the projected innerdiameter side opening portions 30 of the plurality of radial holes 15may be positioned within the area (in the dotted line S of FIGS. 4A and4B) of two circles L formed by connecting each of the axial end portionsof the respective pockets P of the retainer 14 in the rotational axialdirection of the ball bearing 10. That is, as illustrated in FIG. 4A, atleast parts of the projected inner diameter side opening portions 30 ofthe plurality of radial holes 15 may overlap with a circle L on thecounter bore side formed by connecting each of the axial end portions ofthe respective pockets P of the retainer 14 in the rotational axialdirection of the ball bearing 10. Alternatively, as illustrated in FIG.4B, at least parts of the projected inner diameter side opening portions30 of the plurality of radial holes 15 may overlap with a circle L on aside opposite to the counter bore side formed by connecting each of theaxial end portions of the respective pockets P of the retainer 14 in therotational axial direction of the ball bearing 10.

When at least parts of the inner diameter side opening portions 30 ofthe radial hole 15 are positioned within the outer ring raceway groove12 a, the inner diameter side opening portions 30 of the radial hole 15are preferably formed at the contact point between the outer ringraceway groove 12 a and the ball 13 when a preload or an external loadis applied to the bearing or when the position which does not interferewith a contact ellipse E. When the radial hole 15 is formed as describedabove, the stress concentration caused by the contact between the edgeportion of the radial hole 15 and the ball 13 can be prevented, and theseparation of the ball 13 or the outer ring raceway groove 12 a can beprevented. Incidentally, the contact ellipse E is contact ellipsegenerated only by the initial preload, and more preferably, the contactellipse is contact ellipse generated by the bearing internal loadincluding the external load generated during machining the workpiece.

With reference to FIGS. 2 to 3C, when the central line X1 of any oneradial hole 15 a of the plurality of radial holes 15 a and 15 bcoincides with the circumferential phase of the center O of the ball 13,two conditions are satisfied which mean that (i) as illustrated in FIG.3A, any other radial hole 15 b is formed such that when the innerdiameter side opening portion 30 of the radial hole 15 b is projected onthe outer circumferential surface of the retainer 14 along the extensionline of the central line X2 of the radial hole 15 b, the projected innerdiameter side opening portion 30 is separated from the ball 13 and theinner circumferential surface of the pocket P when viewed from theracial direction of the ball bearing 10, and (ii) as illustrated in FIG.3B, the central line X2 of any other radial hole 15 b overlaps with thepocket P when viewed from the axial direction of the ball bearing 10. Inaddition, as illustrated in FIGS. 3A and 3B, the positions of the otherradial hole 15 b and the central line X2 of the other radial hole 15 bmay be the positions of 15 b′ and X2′ in the drawings, respectively.

That is, in the condition (i), the above-described projected innerdiameter side opening portion 30 of any other radial hole 15 b can bearranged within the area F of FIG. 3A. In addition, the central line X2of the other radial hole 15 b is positioned to be separated from theline C passing through the center O of the ball 13. Incidentally, inFIGS. 3A to 3C, “d” indicates the hole diameter of the radial hole 15 b.

In the outer ring oil supply system, when the radial hole 15 is presentin the outer ring raceway groove 12 a, and the ball 13 passes on theradial hole 15 during bearing rotation, the radial hole 15 is closedphysically. Accordingly, the vibration and the noise are generated. Thisvibration is air vibration generated by periodically repeating aphenomenon in which (1) the radial hole 15 is closed when the ball 13passes just on the radial hole 15 to block the flow of the compressedair, and then (2) the flow restarts after the ball 13 passes just on theradial hole 15.

The air vibration tends to become larger as the number of the balls 13passing on the radial holes 15 once increases, and when the vibrationincreases, the noise increases, and the machining accuracy of thespindle is deteriorated.

Particularly, the noise is known to be a notable problem. In the areawhere the outer ring oil-supply type bearing is used mainly, and thenumber of revolutions is 10000 min⁻¹ or more, a problem easily occurs inwhich the frequency of the generated noise is about several thousand Hz,and the noise of the frequency band in which the sensitivity of thehuman ears is the highest is generated.

When the plurality of radial holes 15 are closed simultaneously by theballs 13, the supply amount of the lubricating oil while passing isreduced remarkably. Further, after the balls 13 pass, the lubricatingoil stored in the radial hole 15 is supplied once. Stirring resistanceof the lubricating oil increases due to instantaneous excessive supplyof the lubricating oil, and thus the temperature of the bearing outerring rises remarkably. Accordingly, the machining accuracy isdeteriorated, or the risk of the seizure due to the abnormal temperaturerise increases.

For this reason, it is desirable that the balls 13 do not pass on theplurality of radial holes 15 simultaneously during bearing rotation.Therefore, when the central line X1 of any one radial hole 15 acoincides with the circumferential phase of the center O of the ball 13,and the inner diameter side opening portion 30 of any other radial hole15 b is projected on the outer circumferential surface of the retainer14 along the extension lines of the central lines X1 and X2 of theradial holes 15, the projected inner diameter side opening portion 30 isseparated from the ball 13 and the inner circumferential surface of thepocket P when viewed from the radial direction of the ball bearing 10.Thus, the central line X2 of other radial hole 15 b is separated fromthe circumferential phase (the line C of FIGS. 3A to 3C) of the center Oof the ball 13. That is, when any one radial hole 15 a is closed by theball 13, the other radial hole 15 b is open so that the flow of thecompressed air is not completely blocked, and the noise and thevibration can be reduced.

Incidentally, when the outer ring 12 includes three or more radial holes15, and the central line X1 of any one radial hole 15 a coincides withthe circumferential phase of the center O of the ball 13, moredesirably, all of the above-described projected remaining other radialholes 15 b are positioned in the area F.

In addition, in the condition (ii), as illustrated in FIG. 3B, thecentral line X2 of any other radial hole 15 b is positioned within thearea Fa overlapping with the pocket P when viewed from the axialdirection of the ball bearing 10. Therefore, in order to satisfy theabove-described two conditions (i) and (ii), when viewed from the radialdirection of the ball bearing 10, the above-described projected innerdiameter side opening portion 30 of any other radial hole 15 b becomesthe area Fb illustrated in FIG. 3C in a case where the hole diameter ofthe radial hole is adopted as illustrated. Further, when the holediameter of the radial hole is changed, the illustrated area Fb ischanged.

Accordingly, the inner diameter side opening portion 30 of the otherradial hole 15 b is arranged to be positioned close to the ball 13 andthe inner circumferential surface of the pocket P. Thus, the lubricatingoil supplied from the other radial hole 15 is supplied to the slidingcontact part between the ball 13 and the inner circumferential surfaceof the pocket P through the outer circumferential surface of theretainer 14, thereby securing stable lubricity.

In the present embodiment, in consideration of the supply of thelubricating oil and the prevention of the interference with the contactellipse E, the diameter of the radial hole 15 is set to 0.5 to 1.5 mm.In the present embodiment, the radial hole 15 has a uniform diameterover the radial direction.

In a bearing device 1 configured in this way, the outer ring 12 includesthe plurality of radial holes 15 which penetrate from the outercircumferential surface to the inner circumferential surface in theracial direction to supply the lubricating oil. Further, when the innerdiameter side opening portions 30 of the plurality of radial holes 15are projected on the outer circumferential surface of the retainer 14along the extension line of the central lines X1 and X2 of the radialholes 15, at least parts of the projected inner diameter side openingportions 30 are positioned within the area of two circles L formed byconnecting each of the axial end portions of the respective pockets P ofthe retainer 14 in the rotational axial direction of the ball bearing10. In addition, when the central line X1 of any one radial hole 15 a ofthe plurality of radial holes 15 coincide with the circumferential phaseof the center O of the ball 13, any other radial hole 15 b is formedsuch that when the inner diameter side opening portion 30 is projectedon the outer circumferential surface of the retainer 14 along theextension line of the central line X2 of the radial hole 15 b, theprojected inner diameter side opening portion 30 is separated from theball 13 and the inner circumferential surface of the pocket P whenviewed from the radial direction of the ball bearing 10, and the centralline X2 of any other radial hole 15 b overlaps with the pocket P whenviewed from the axial direction of the ball bearing 10. Accordingly, thelubricating oil is supplied from any one radial hole 15 a to the slidingcontact part between the ball 13 and the retainer 14, and also from anyother radial hole 15 b, sufficient lubricating oil is supplied to thesliding contact part between the ball 13 and the retainer 14 through theouter circumferential surface of the retainer 14. Therefore, theexcellent lubricating state can be maintained to prevent the seizure ofthe bearing. In addition, the noise and the vibration can be reducedwithout completely blocking the flow of the compressed air.

In the present embodiment, as in a first modification illustrated inFIG. 5, in the outer circumferential surface of the outer ring 12,annular grooves 19 may be formed on both axial sides sandwiching theconcave groove 16 along the circumferential direction, and a seal member20 which is an annular elastic member such as an O ring may be arrangedin each of the annular grooves 19, thereby preventing the oil leakage.

In the present embodiment, the projected inner diameter side openingportions 30 of the radial holes 15 may be within the range illustratedin an area S of FIG. 1. In FIG. 1, the inner diameter side openingportion 30 is formed on the counter bore side regarding a groove bottomA of the outer ring raceway groove 12 a. As in a second modificationillustrated in FIG. 6, the inner diameter side opening portion 30 may beformed on a side opposite to the counter bore side with respect to thegroove bottom A of the outer ring raceway groove 12 a. In addition, anyone radial hole 15 may be formed on the counter bore side with respectto the groove bottom A of the outer ring raceway groove 12 a, and anyother radial hole 15 may be formed on a side opposite to the counterbore side with respect to the groove bottom A of the outer ring racewaygroove 12 a.

The radial hole 15 may penetrate from the outer circumferential surfaceof the outer ring to the inner circumferential surface in the radialdirection. The radial hole may be formed along the radial direction(parallel to a radial sectional plane) of the present embodiment or maybe formed to be inclined in the rotational axial direction or thecircumferential direction of the bearing. For example, as in a thirdmodification illustrated in FIG. 7, the radial hole 15 may be formed tobe bent in the axial direction in the middle of the radial direction ofthe bearing.

As in fourth and fifth modifications illustrated in FIGS. 8A and 8B, theradial hole 15 may be formed such that the opening area of the innerdiameter side opening portion 30 is wider than the opening area of anouter diameter side opening portion 31. In the fourth modification, thediameter of the radial hole 15 is enlarged such that the area isgradually enlarged from the outer diameter side opening portion 31 tothe inner diameter side opening portion 30. In the fifth modification,the radial hole 15 is formed in a stepped shape such that the openingarea of the inner diameter side opening portion 30 is larger than theopening area of the outer diameter side opening portion 31. That is, inthe outer ring oil-supply type rolling bearing, the lubricating oil isdirectly supplied to the ball 13 through the radial hole 15. Thus,although the supply air pressure is lowered near the inner diameter sideopening portion 30, the lubricating oil can be supplied to the ball 13.For this reason, by lowering the air pressure of the inner diameter sideopening portion 30, the collision of the high-pressure air against theball 13 can be prevented, and the noise during the rotation of thebearing can be reduced.

In the second to fifth modifications illustrated in FIGS. 6 to 8B, theseal member 20 is arranged in the outer circumferential surface of theouter ring 12. However, similarly to FIG. 1, the seal member may not beprovided.

The invention is not limited to the above-described embodiments and maybe modified or improved appropriately.

Oil-mist lubrication may be adopted in addition to the oil-airlubrication as a method of supplying the lubricating oil into the racialhole of the outer ring. In some cases, oil jet lubrication may beadopted. However, in a grease supplying method of supplying grease fromthe radial hole 15 of the outer ring 12 by using the lubricant supplyingdevice around the bearing or outside the spindle, when the radial hole15 is formed to be open in the outer ring raceway groove 12 a, thegrease which is a semisolid containing a thickener is supplied into theouter ring raceway groove 12 a.

In this case, since the grease is bitten into the outer ring racewaygroove 12 a, the stirring resistance causes problems such as theincrease of the torque and the abnormal heat generation. Particularly,these problems easily occur in the high-speed rotation as in the presentembodiment. Therefore, an oil lubricating method of supplying thelubricating oil not containing the thickener is desirable in theinvention.

The ball bearing of the invention is not limited to those applied to thespindle device for the machine tool and may be applied as a ball bearingof a general industrial machine or a high-speed rotating device such asa motor.

This application is based on Japanese Patent Application No. 2016-153246filed on Aug. 3, 2016, the contents of which are incorporated herein byreference.

DESCRIPTION OF REFERENCE NUMERALS

-   -   10: angular ball bearing (ball bearing)    -   11: inner ring    -   11 a: inner ring raceway groove    -   12: outer ring    -   12 a: outer ring raceway groove    -   12 b: counter bore    -   12 c: groove shoulder    -   13: ball    -   14: retainer    -   15, 15 a, 15 b: radial hole    -   16 concave groove    -   E: contact ellipse

1. A ball bearing comprising: an inner ring with an inner ring racewaygroove on an outer circumferential surface; an outer ring with an outerring raceway groove on an inner circumferential surface; a plurality ofballs which are arranged in a rollable manner between the inner ringraceway groove and the outer ring raceway groove; and a retainer with aplurality of pockets for retaining the plurality of respective balls,wherein: the outer ring includes a plurality of radial holes whichpenetrate from the outer circumferential surface to the innercircumferential surface in the radial direction to supply lubricatingoil, such that the ball bearing is lubricated by the lubricating oil;when inner diameter side opening portions of the plurality of radialholes are projected on an outer circumferential surface of the retaineralong extension lines of central lines of the radial holes, at leastparts of the projected inner diameter side opening portions arepositioned within an area of two circles formed by connecting each ofaxial end portions of respective pockets of the retainer in a rotationalaxial direction of the ball bearing; and when the central line of anyone radial hole among the plurality of radial holes coincides with acircumferential phase of a center of the ball, any other radial hole isformed such that when the inner diameter side opening portion of theother radial hole is projected on the outer circumferential surface ofthe retainer along the extension line of the central line of the radialhole, the projected inner diameter side opening portion is separatedfrom the ball and the inner circumferential surface of the pocket whenviewed from a radial direction of the ball bearing, and the central lineof the other radial hole overlaps with the pocket when viewed from theaxial direction of the ball bearing.
 2. The ball bearing according toclaim 1, wherein a concave groove communicating with the radial hole isformed along a circumferential direction in an outer circumferentialsurface of the outer ring.
 3. The ball bearing according to claim 2,wherein in the outer circumferential surface of the outer ring, annulargrooves are formed on both axial sides sandwiching the concave groovealong the circumferential direction, and annular seal members arerespectively arranged in each of the annular grooves.
 4. The ballbearing according to claim 1, a diameter of the radial hole is 0.5 to1.5 mm.
 5. The ball bearing according to claim 1, in the radial hole, anopening area of the inner diameter side opening portion is larger thanan opening area of the outer diameter side opening portion.
 6. A spindledevice for a machine tool comprising: the ball bearing according toclaim 1
 7. A spindle device for a machine tool comprising: the ballbearing according to claim
 2. 8. A spindle device for a machine toolcomprising: the ball bearing according to claim
 3. 9. A spindle devicefor a machine tool comprising: the ball bearing according to claim 4.10. A spindle device for a machine tool comprising: the ball bearingaccording to claim 5.